This invention relates to the art of thread cutting tools and, more particularly, to improvements in connection with thread cutting diestock assemblies of the character comprising a rotatable head member and thread cutting tools detachably associated therewith.
The present invention finds particular utility in connection with diestock assemblies wherein the head member and detachable tools cooperatively define a ratchet and pawl arrangement by which the thread cutting tools are driven in response to rotation of the head and, accordingly, the invention will be described in detail in conjunction with such a ratchet and pawl drive arrangement. At the same time, however, it will be appreciated that the invention is applicable to the detachable inter-engagement of tools and heads wherein the tools are driven other than by a ratchet and pawl arrangement.
Diestock assemblies comprising a head in the form of a ratchet housing for detachably receiving thread cutting die heads are of course well known and advantageously provide a rotatable thread cutting tool capable of cutting threads on a variety of different size workpieces such as pipes and rods. Such diestock assemblies are shown, for example, in U.S. Pat. No. 2,004,639 to Thewes, and U.S. Pat. No. 4,213,723 to Wagner. In Thewes, each of a set of die heads is detachably received in a driven ratchet ring mounted in the ratchet housing and in Wagner, the ratchet housing is adapted to directly drive either a first set of die heads or an adaptor ring, each of which is detachable received therein, and the adaptor ring is adapted to detachably receive and drive a second set of die heads, whereby a single ratchet housing accommodates thread cutting die heads for cutting threads on a wider variety of sizes of workpieces. The exterior of the ratchet ring in Thewes and the exteriors of the adaptor ring and large die head in Wagner are provided with ratchet teeth engaging a pawl carried in the ratchet housing, whereby the ratchet ring, adaptor ring or large die head is rotated in response to displacement of the ratchet housing in the direction to drivingly engage the pawl and teeth. The bores in the ratchet ring and adaptor ring are of polygonal cross-section to receive a correspondingly contoured part of the die head received therein, whereby the latter is rotated with the ratchet ring or adaptor ring.
Heretofore, as will be seen in the Thewes and Wagner patents, detachability between the ratchet housing and the adaptor ring or large die head is achieved through the use of a circular split retaining spring ring which is generally rectangular in cross-section, and detachability between the die head and the ratchet ring or adaptor ring is achieved through the use of a circular split retaining spring ring which is circular in cross-section. In connection with the retaining ring in Wagner by which the adaptor ring or large die head is detachably secured in the ratchet housing, the retaining ring is carried in an annular recess or groove in the removable part and engages the latter against a shoulder in the ratchet housing, and in connection with the retaining rings in Thewes and Wagner by which a die head is detachably secured in the polygonal bore in the ratchet ring or adaptor ring, the retaining ring is carried in an annular recess or groove in the polygonal bore. Portions of the latter retaining ring span the corners between adjacent wall portions of the bore, and the spanning portions are engaged and radially outwardly displaced by corners on the polygonal coupling portion of the die head during movement of the die head into the bore. The retaining ring then constricts into a groove therefor in the die head to detachably secure the latter in place.
A number of problems and disadvantages are attendant to the use of such retaining ring arrangements heretofore provided. In this respect, with regard to the retaining ring between the ratchet housing and adaptor ring of Wagner, the retaining ring must be pried from the recess in which it is carried, through the use of an appropriate tool, in order to separate the large die head or adaptor ring from the ratchet housing, and the ring must then be reassembled with respect to the component which replaces the removed component. Thus, the removing and reassembling operations are time consuming, and the separation of the retaining ring by prying and the replacement thereof each time a part is to be interchanged with the ratchet housing necessarily imposes undesirable stresses on the ring and wearing engagement between the surfaces of the parts. With regard to the retaining ring between the ratchet ring or adaptor ring and the smaller die heads, extreme accuracy in the unexpanded diameter of the ring is required to assure adequate retention of the die head in the adaptor or ratchet ring bore and to preclude jamming therebetween. In this respect, if the retaining ring diameter is on the large side it will not sufficiently retain the die head against axial separation from the ring and, if the retaining ring diameter is on the small side, it can shift laterally and/or circumferentially relative to the recess or groove in which it is carried such that the ring is misaligned with the axis of the bore and/or the ends of the spring are exposed radially inwardly of the ratchet ring or adaptor ring bore. Either of these conditions results in impeding introduction of the die head past the spring, and exposure of the spring ring ends can cause displacement of the retaining ring out of its groove or recess by the die head. Moreover, exposure of the ends of the retaining ring radially inwardly of the adaptor ring bore can result in jamming of the die head when assembled therewith, thus making separation of the die head difficult and subjecting the coupling portion thereof to damage.